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Abstract:

The present invention is related to a porous structure material, which is
synthesized by mixing an alkyl siloxane compound or a silicate compound
with an organic solvent through a sol-gel process, and modified by
modification agents. The present invention is also related to a method
for manufacturing porous structure material, which comprises reacting an
alkyl siloxane compound or a silicate compound with an organic solvent
through sol-gel process. The present invention utilizes modification
agents to modify hydrophilic groups into hydrophobic groups on the
surface of the porous structure material, thereby to lower the surface
tension and maintain the porous structure. The porous structure material
of the present invention has properties of low conductive coefficient,
high porosity, high hydrophobicity and self-cleaning.

Claims:

1. A porous structure material, which is synthesized by mixing an alkyl
siloxane compound or a silicate compound with an organic solvent through
a sol-gel process, and modified by modification agents; wherein said
modification agents comprises a mixture of trimethylchlorosilane/n-hexane
or a mixture of dimethylchlorosilane/n-hexane, and said porous structure
material has average thermal conductive coefficient of 0.04 W/m-K to 0.02
W/m-K.

2. The porous structure material according to claim 1, wherein the surface
of said porous structure material comprises hydrophobic groups.

3. The porous structure material according to claim 1, wherein the mixing
ratio of the alkyl siloxane compound or the silicate compound to the
organic solvent is 1:6 to 1:10.

4. The porous structure material according to claim 1, wherein the bulk
density of said porous structure material is higher than 0.069
g/cm.sup.3.

5. The porous structure material according to claim 1, wherein the
porosity of said porous structure material is higher than 95%.

6. A method for manufacturing a porous structure material, which
comprises:(a) mixing an alkyl siloxane compound or a silicate compound
with an organic solvent;(b) adding acidic catalyst to proceed hydrolysis
reaction;(c) adding basic catalyst to proceed condensation reaction, and
forming a sol;(d) washing said sol by a solvent;(e) exchanging the
solvent within said sol with an organic solvent;(f) adding modification
agents to modify the surface of said sol, in which said modification
agents comprise a mixture of trimethylchlorosilane/n-hexane or a mixture
of dimethylchlorosilane/n-hexane;(g) removing the modification agents
within said sol; and(h) drying the sol in step (g) to produce a porous
structure material.

7. The method according to claim 6, wherein the alkyl siloxane compound in
step (a) comprises tetraethoxysilane or tetramethoxysilane.

13. The method according to claim 6, wherein the organic solvent in step
(e) comprises n-hexane or heptane.

14. An applicable material comprising the porous structure material
according to claim 1, which is used for coating agent, filling material,
and heat insulating material.

15. The applicable material according to claim 14, which has bulk density
of higher than 0.069 g/cm.sup.3.

16. The applicable material according to claim 14, which has porosity of
higher than 95%.

17. The applicable material according to claim 14, which has average
thermal conductive coefficient of 0.04 W/m-K to 0.02 W/m-K.

Description:

BACKGROUND OF THE INVENTION

[0001]1. Field of the invention

[0002]The present invention is related to a porous structure material
comprising an alkyl siloxane, and to a method for preparing said
material, especially for utilizing modifying agents to modify hydrophilic
groups into hydrophobic groups on the surface of said porous structure
material, thereby to lower the surface tension, thermal conductive
coefficient and density, to enhance the porosity, and to produce a
material having high heat insulating property.

[0003]2. Description of the related art

[0004]The porous material of silica aerogel has the same chemical
components as glass, and said material has advantages such as low
density, low refractive index, high BET surface area, small pore size,
and within the visible light spectrum. Such material has obvious
commercial value to be applied in associated technologies, such as glass
bulk material and optic fiber derived from gel, solar energy storage
system, heat preservation system of furnace, heat preservation tube,
filling material, radioluminescence and power system, the catalysis and
filtration of polluted air/water, and transparent/opaque heat insulating
material, thereby can improve the energy saving and enhance economic
value in light of energy shortage.

[0005]The preparation of the above-mentioned aerogel mainly comprises:
homogenously mixing an alkyl siloxane or a silicate with various
solvents, drying, and then producing a porous network nano-structure
material having low density and low thermal conductive coefficient. A
porous material of having nano pores, which is produced by silica
aerogel, has extreme low material density because air occupies 80% and
more of the volume in the three-dimensional network structure of said
aerogel. The aerogel itself is transparent or semi-transparent, and it
has excellent heat insulating effect because the air having refractive
index of 1 occupies most volume of the aerogel, and thereby said aerogel
has particular properties such as light weight, low refractive index and
low thermal conductive coefficient.

[0006]However, if the aerogel is synthesized through sol-gel process, it
is known that the aerogel will be broken by the contraction resulted from
high surface tension, in which the surface tension is produced by
hydrophilic groups --OH when the aerogel contacts the air and the ambient
pressure drying is proceeded; therefore, the network structure inside the
dried aerogel will be collapsed, the aerogel itself will be broken, and
the aerogel will lose the advantage from low thermal conductive
coefficient. Since then, it will be obviously advantageous if we can find
a method for lowering the high surface tension of the aerogel because the
gel contraction, thermal conductive coefficient, density of the aerogel,
and enhancing the porosity of said gel will be decreased.

SUMMARY OF THE INVENTION

[0007]The materials having high insulating property cannot be produced by
the conventional aerogel preparation process because the structure of
said material often collapses, which resulted from the contraction of
framework and the surface tension of the nano pores within the gel during
the drying step, and thereby the thermal conductive coefficient
increases. Therefore, one object of the present invention is to provide a
porous structure material synthesized by mixing an alkyl siloxane
compound or a silicate compound with an organic solvent through a sol-gel
process, and the hydrophilic groups located on the surface of the porous
structure material are modified into hydrophobic groups by modification
agents. The porous structure material will not absorb the water in the
air easily, so the damage of the porous structure will be avoided, and
the disadvantages of the conventional porous material caused by extreme
high surface tension, e.g. high density, high thermal conductive
coefficient, low porosity, and low hydrophobicity, will be overcome.

[0008]Another object of the present invention is to provide a method for
manufacturing a porous structure material, which is used for preparing a
porous structure material having low density, low thermal conductive
coefficient, high porosity, high hydrophobicity and the like.

[0009]Yet another object of the present invention is to provide an
applicable material having low density and low thermal conductive
coefficient, which is used for coating agent, filling material, and heat
insulating material.

[0010]To achieve the above mentioned objects, the present invention
provides a porous structure material synthesized by mixing an alkyl
siloxane compound or a silicate compound with an organic solvent through
a sol-gel process, and modified by modification agents; wherein said
modification agents comprises a mixture of trimethylchlorosilane/n-hexane
or a mixture of dimethylchlorosilane/n-hexane, and said porous structure
material has average thermal conductive coefficient of 0.04 W/m-K to 0.02
W/m-K. The surface of said porous structure material comprises
hydrophobic groups.

[0011]In some preferred embodiments, the mixing ratio of the alkyl
siloxane compound or the silicate compound to the organic solvent is 1:6
to 1:10.

[0012]In some preferred embodiments, the bulk density of said porous
structure material is higher than 0.069 g/cm3, and the porosity of
it is higher than 95%.

[0013]Also, the present invention provides a method for manufacturing a
porous structure material, which comprises: (a) mixing an alkyl siloxane
compound or a silicate compound with an organic solvent; (b) adding
acidic catalyst to proceed hydrolysis reaction; (c) adding basic catalyst
to proceed condensation reaction, and forming a sol; (d) washing said sol
by a solvent; (e) exchanging the solvent within said sol with an organic
solvent; (f) adding modification agents to modify the surface of said
sol, in which said modification agents comprise a mixture of
trimethylchlorosilane/n-hexane or a mixture of
dimethylchlorosilane/n-hexane; (g) removing the modification agents
within said sol; and (h) drying the sol in step (g) to produce a porous
structure material.

[0014]In some preferred embodiments, the alkyl siloxane compound in step
(a) comprises tetraethoxysilane or tetramethoxysilane; the organic
solvent in step (a) comprises anhydrous ethanol, isopropanol, acetone,
methanol, formamide, or ethylene glycol; and the mixing ratio of the
alkyl siloxane compound or the silicate compound to the organic solvent
in step (a) is 1:6 to 1:10.

[0019]The present invention also provides an applicable material
comprising said porous structure material, which is used for coating
agent, filling material, and heat insulating material.

[0020]In some preferred embodiments, said applicable material has bulk
density of higher than 0.069 g/cm3, porosity of higher than 95%, and
average thermal conductive coefficient of 0.04 W/m-K to 0.02 W/m-K.

[0021]By adding modification agents, the present invention can modify the
hydrophilic groups on the surface of the gel into hydrophobic groups and
lower the surface tension, and thereby the gel can maintain its complete
network structure during the drying step. The porous structure material
manufactured by the present invention has low density, low thermal
conductive coefficient, high porosity, high hydrophobicity, and other
advantages that the material produced by the conventional producing
method cannot have.

BRIEF DESCRIPTION OF THE DRAWINGS

[0022]FIG. 1 is the diagram illustrating the principle of the present
invention.

[0023]FIG. 2 is the flow chart of the porous aerogel preparation described
in example 1 of the present invention.

[0024]FIG. 3 is the IR spectrum of the porous aerogels described in
example 2 of the present invention.

[0025]FIG. 4 is the electro-microscopic photo of the modified porous
aerogel described in example 2 of the present invention.

[0026]FIG. 5 is the diagrams illustrating the contact angles of the
modified porous aerogels described in example 2 of the present invention;
wherein (A) is single-modified porous aerogel, and (B) is
multiple-modified porous aerogel.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0027]In conventional aerogel preparation, the surface of the gel is
usually hydrophilic, as shown in the following formula (I); therefore,
when said gel contact the air, it will absorb the water in the air,
thereby damage the porous structure of the gel, lower the insulating
property, and result in inability to use for a long time, and lack of
weatherability and continuous usability. In addition, when the ambient
temperature is extreme high, the thermal conductive coefficient of the
aerogel will result in the steep decrease in insulating effect, so the
gel cannot be used under high temperature.

[0028]Generally speaking, the functional groups on the surface of the
aerogel prepared by alkyl siloxane or silicate are mainly --OH groups.
When such hydrophilic groups contact with the air, the aerogel will be
broken by the contraction resulted from high surface tension. Therefore,
in order to proceed the drying step under normal pressure, the inventor
have done some research and found that the surface modification
technology can modify the hydrophilic groups on the surface of the wet
gel into hydrophobic groups, and dramatically decrease the effect of
surface tension, thereby the dried aerogel can still maintain its
complete three-dimensional network structure.

[0029]The surface modification agents for general use are
trimethylchlorosilane (TMCS) and dimethylchlorosilane. The --OH groups on
the surface of the aerogel will react with the --Cl groups of
modification agents and produce hydrochloric acid, thereby the H of said
--OH groups will be replaced, that is, the --OH groups are modified to
hydrophobic --OSi(CH3)3 groups, as shown in the following
formula:

[0030]In addition, the thermal conductive coefficient of the aerogel
having finely solid network structure can be represented by the following
formula:

k's=ρ'ν'[ks/(ρsνs)]

[0031]In said formula, ρ' and ρs represent the density of
each gel and the bulk density of the solid respectively; ν' and
νs represent the longitudinal sound velocity of each gel and the
sound velocity of the solid; κs is the thermal conductive
coefficient of the solid.

[0032]To the solid thermal conductive coefficient of the material having
full density and being formed the network structure, k's, the main
variants are ρs, νs, κs. The ratio
ks/(ρsνs) will change according to the selection of
aerogel material. If the lower k's is desired, choosing an aerogel
having high density, low thermal conductive coefficient, and high sound
velocity is necessary.

[0033]The present invention is characterized by homogeneously dispersing
the gel particles in a solution by an alkyl silicone during the stage of
sol; maintaining the relative activity of the particles; and making them
to polymerize to a gel having larger molecular weight; catalyzing the gel
to a wet gel by various catalysts; and then drying to leave an aerogel
insulating material having low density, low thermal conductive
coefficient, and a porous network nano structure. (See FIG. 1)

[0034]The following Examples are provided to specifically describe the
technical features of the present invention, but these Examples are not
used to limit this invention, and various alterations and modifications
can be made by those skilled in the art without departing from the spirit
and the scope of this invention.

EXAMPLES

Example 1,

Preparing of a Modified Porous Aerogel

[0035]This example is to produce an aerogel insulating material having a
porous network nano structure, and the flow chart of this preparation is
shown in FIG. 2. First, by sol-gel process, mixing a precursor material
and an organic solvent; adding acidic catalyst to proceed hydrolysis
reaction; adding basic catalyst to proceed condensation reaction, and
forming a sol. The sol is extreme small gel particles, and said gel
particles are homogeneously dispersed in the solution. Next, the
molecules with in the sol will be further condensed to produce bonds, and
form a semi-solid high molecular gel. After aging for a period of time,
said gel will form a stable three-dimensional network structure.

[0036]The precursor material of this example is tetraethoxysilane (TEOS).
To proceed the hydrolysis and condensation reactions through sol-gel
process, tetraethoxysilane, anhydrous ethanol, and deionized water are
used as the sol body, and hydrochloric acid and ammonia are used as
acidic catalyst and basic catalyst respectively. The mixing process in
two separate stages (referring to FIG. 2, adding HCl and NH4OH), and
each homogeneously mix 120 minutes, finally to form a sol.

[0037]Then the sol is sealed and static tested at room temperature
(25° C.) to proceed gelation. After four-day aging, a wet gel is
formed. After that, the wet gel is washed by high purity ethanol (99%) at
60° C. once a day for three days.

[0038]Subsequently, the static solvent within the gel is exchanged with
n-hexane at 60° C. for four times, each time for 24 hours (one
day). The modification agents, trimethylchlorosilane (TMSC) and n-hexane,
are prepared by solving 6% TMSC in n-hexane, and the wet gel modification
is proceeded statically at 25° C. for four times, each time for 24
hours (one day). After the static modification, the gel is washed at
25° C. by n-hexane for four times, each time for 24 hours (one
day), to remove the modification solvent within the modified gel. At
last, the wet gel is dried for 96 hours under room temperature and normal
pressure, to produce a heat insulating aerogel material having a porous
network nano structure.

[0039]Notice should be added that the modification steps described above
is single-modification process, and single-modification repeated several
times means multiple-modification.

[0040]In this example, there is another experiment group which process
multiple-modification and the difference between single-modification and
multiple-modification is the number of times for modification. In
single-modification, the gel is soaked in the modification agents for 24
hours, and then washed. In multiple-modification, the gel is soaked in
the modification agents for 24 hours and the reaction balance is reached,
then more fresh modification agents are added, and the modification step
is repeating to reach complete surface modification, that is, all silica
particles within the holes are modified to hydrophobic. The illustrative
structure of the modified porous aerogel according to this example is as
following:

[0041]wherein the ratio of Si--O--Si to OSi(CH3)3 is
approximately 1:4.

[0042]The skilled in the art can change various control parameters
including the molar ratio of reactants, acidic catalyst, basic catalyst,
reaction temperature, molar content of the solvents, stirring speed,
mixing time, modification agents, pH, drying time, and the like to
proceed the sol-gel process.

Example 2

Testing Characteristics of the Porous Aerogel

[0043]In this Example, the density, porosity, volume shrinkage, thermal
conductive coefficient, BET surface area, average pore size, and average
pore volume of the unmodified gel and the modified gels according to
Example 1 are tested, and the structure and components of said gels are
observed by IR and electro-microscopy. The tests of the present invention
are proceeded according to the dead volume method developed in Japan,
which is used as a pore structure analyzing method for porous materials.

[0044]The characteristics of the unmodified gel and the modified gels
according to Example 1 are shown in Table 1. From these results, after
multiple-modification, the density of the aerogel decreases to about
0.069 g/cm3, the porosity increases to about 97%, the BET surface
area increases, the total pore volume increases obviously, and the
average pore size also become larger.

[0045]The IR spectrum of the unmodified gel and the modified gels
according to Example 1 is shown in FIG. 3, in which the signals of
Si--O--Si appear at 1080 cm-1 and 450 c-1, the signals of
Si--OH appear at 3450 cm--1, and 965 cm-1, the signals of
CH3 of Si(CH3)3O-- appear at 2980 cm-1 and 845
cm-1, and the signal of H--OH appears at 1632 cm-1. As the
arrows shown in FIG. 3, the unmodified gel has signals at 3450 cm-1
and 965 cm-1 (from Si--OH groups), also has an obvious signal at
1632 cm-1 (from H--OH groups), but it has no signal at 2980
cm-1 and 845 cm-1 (from CH3 groups). These results show
that the unmodified gel has Si--OH groups and H--OH groups, but it does
not have CH3 groups comprised in the modification agents. On the
contrary, when the aerogel is single-modified or multiple modified gel,
the signals at 3450 cm-1 and 965 cm-1 (from Si--OH groups)
disappear as the number of times for modification increases, the signals
at 2980 cm-1 and 845 cm-1 from CH3 of
Si(CH3)3O-- appear as the number of times for modification
increases, and the signals at 1080 cm-1 and 450 cm-1 from
Si--O--Si become more obvious. These changes show that the hydrophilic
groups of modified aerogels have been exchanged with hydrophobic groups.

[0046]In addition, the H--OH signal, which represents that water is
comprised in the gel, appears in unmodified aerogel, but not appear in
single-modified or multiple-modified aerogel. This shows that the water
content in the modified aerogels is extreme low.

[0047]The pore and pore size of the modified gel according to Example 1
are shown in FIG. 4. This shows that the modified aerogel has a complete
porous structure, and the problem that the structure of the conventional
aerogel collapses is resolved. From above, we know that the surface
tension can be effectively decreased by surface modification technology
that modifies the hydrophilic groups on the surface of the wet gel to
hydrophobic groups, thereby the dried aerogel can maintain a complete
three-dimensional network structure.

[0048]To understand the difference of thermal conductivity between the
single-modified and multiple-modified aerogel, the hydrophobic angle test
is preceded, and the results are shown in Table 2 and FIG. 5. In FIG. 5,
(A) shows the contact angle of a single-modified aerogel and (B) shows
the contact angle of a multiple-modified aerogel. When the number of
times for modification increases, the thermal conductive coefficient will
decrease and the contact angle becomes larger which means hydrophobic
increases. This can explain why the multiple-modified aerogel having
higher hydrophobicity makes the contact angel increase.

[0049]In summary, the present invention uses modification agents, e.g.
trimethylchlorosilane, to modify the hydrophilic groups on the surface of
the aerogel to hydrophobic groups, thereby the surface tension decreases
and the gel maintains a complete three-dimensional network structure in
the drying step. Therefore, the porous material produced by the process
of the present invention has low density, low thermal conductive
coefficient, high porosity, high hydrophobicity, and the like, and it has
excellent effect for being used as heat insulating materials, heat
preservation materials, dew-preventing materials, fireproof materials,
corrosion resistant materials.

[0050]Although the preferred Examples of the present invention are
disclosed above, but they are not used to limit the scope of this
invention. Various alterations and modification can be done by those
skilled in the art without departing from the spirit and the scope of
this invention. The scope of the present invention is defined by the
appended claims.

Other Embodiments

[0051]The present invention is specifically described in the
above-mentioned Examples, and various alterations and modification can be
done without departing from the spirit and the scope of this invention by
those skilled in the art according their needs. Therefore, other
embodiments are also included in the scope of this invention.